Introduction of five key problems of sodium-sulfur battery

At present, there are some doubts about the sodium-sulfur battery, and it is considered that the sodium-sulfur battery is difficult to be commercially realized in the short term. To this end, the "Science Times" reporter interviewed the research and development of sodium-sulfur batteries on these issues - researcher Wen Zhaoyin, Liu Yu, senior engineer Cao Jiadi, etc., Shanghai Institute of Ceramics, Chinese Academy of Sciences.

Question 1: Security issues

"The security issue is more accurately said to be a question of operational reliability."

Question: The operating temperature of sodium-sulfur battery is between 300 and 350 °C. If the ceramic dielectric is broken and short-circuited, the high-temperature liquid sodium and sulfur will be in direct contact, and a strong exothermic reaction will occur, resulting in a high temperature of 2000 °C, which is quite dangerous. .

Wen Zhaoyin: Since the demonstration operation in 1992, NGK has operated more than 100 sodium-sulfur battery energy storage power stations in Japan. During the 18-year period, there was only one fire accident and it was extinguished by itself before the fire brigade arrived. It was assessed as a minor accident. .

After commercialization of sodium-sulfur batteries, the Japanese media conducted a large number of publicity reports, hoping to change the public's concept and accept sodium-sulfur batteries.

In fact, any energy storage system is an energy gathering system, and there are security risks. Since ceramic is used as a solid diaphragm, no gas is present and therefore does not explode. Compared with some other batteries, the sodium-sulfur battery accident rate is very low.

Once the sodium and sulfur are in direct contact, there is a safety hazard. Therefore, we have taken a lot of safety measures in the structural design, and the layers are fortified to ensure that even ceramic damage will not be easily touched, even if the battery is damaged, it will not simply overflow.

The sodium-sulfur battery of the silicate plant has not had a safety accident and is undergoing long-term reliability verification.

Question 2: Life issues

“Once the use of practical materials and components, the product life can reach 10 years.”

Question: Short life expectancy affects its cost performance and is difficult to commercialize.

Wen Zhaoyin: Unlike other batteries, sodium-sulfur batteries have no side reactions, and active substances can be used reversibly without being lost. Since metal parts will corrode and work for a long time under high temperature in sulfur and sulfide medium, the metal parts of the sodium-sulfur battery are protected by special anti-corrosion measures.

The life expectancy of the sodium-sulfur battery currently tested by silicate is 8 years, and the initial degradation attenuation level is basically similar to that of Japan. Once in the industrialization stage, the consistency of materials and batteries is solved, and the battery life can reach more than 10 years. At present, the level of Japanese products is about 15 years.

Question 3: Temperature problem

“The module has a very good thermal insulation function and can maintain low power operation for a period of time.”

Question: The sodium-sulfur battery can be started at 300 °C, and there is a problem of insulation energy consumption. The long startup time limits its application to a certain extent.

Cao Jiadi: The sodium-sulfur battery absorbs energy during charging and requires additional electrical energy to heat up. It dissipates heat while discharging, enough to maintain the temperature required for operation.

At the same time, the battery module developed by silicate has a good heat preservation function and can be kept for a long time without power supply heating. At present, it takes about half a month for NGK's products to cool from the operating temperature to room temperature, and maintain low-power operation one week after the power failure.

Question 4: Waste battery disposal problem

“Japan has developed a fairly mature recycling technology.”

Question: Damaged batteries are difficult to handle, which is one of the soft ribs of sodium-sulfur batteries.

Liu Yu: Sodium-sulfur batteries are different from other batteries and are detachable batteries. Therefore, in principle, the recycling rate will be higher. Ceramic parts are incompatible with sodium and sulfur. After use, they can be completely separated and recycled separately. The sodium and sulfur moiety compounds can be reversibly decomposed to form sodium and sulfur; other metal parts can also be recycled.

Japan has now formed a fairly mature recycling technology and process. At present, silicates have initially formed a clean recycling technology process, which is split in some protective media, and sodium, sulfur and metals can be recycled or reused.

However, how to truly recycle and reuse sodium-sulfur batteries in China requires further research.

Question 5: Cost issues

"Our price will not be higher than Japan."

Question: Can the cost of domestic sodium-sulfur batteries be reduced to commercial levels?

Wen Zhaoyin: At present, in various large-capacity energy storage batteries, in addition to low-performance lead-acid batteries, sodium-sulfur batteries are the cheapest. According to Japanese data, the price of lithium-ion batteries is three times that of sodium-sulfur batteries. The flow battery is also more expensive than the sodium-sulfur battery, so the cost of the sodium-sulfur battery is more advantageous.

Moreover, since the raw materials of sodium, sulfur and ceramics are abundant in natural reserves and low in cost, and sodium and sulfur have no special use, the potential factors affecting price fluctuations are relatively small.

China has not yet implemented large-scale applications, so the price is difficult to determine. The space for future cost reduction depends mainly on the scale of industrialization and manufacturing technology.

The current price of NGK products is 2000~2500 yuan/kWh. Our prices will not be higher than abroad.

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